1. Field of the Invention
This invention relates to techniques for increasing breakdown voltage of a semiconductor device.
2. Description of the Background Art
Various types of techniques for increasing breakdown voltage of a semiconductor device have been conventionally proposed. For example, a technique for increasing breakdown voltage of a diode element is proposed by a publication entitled “Improved device ruggedness by floating buffer ring,” The 12th International Symposium on Power Semiconductor Devices & Ics, 2000, pp. 153 to 156, by A. W. Ludikhuize, et al. (hereinafter referred to as “Ludikhuize document”). Also, techniques for increasing breakdown voltage of a semiconductor device are disclosed in Japanese Patent Application Laid-Open Nos. 2003-092414 and 2001-237437.
In the semiconductor device described in the Ludikhuize document, a breakdown voltage in a thickness direction was not always ensured to a sufficient degree.